ci: make clean before building

Author: doyougnu

.github/workflows/deploy.yml

@@ -13,7 +13,7 @@ jobs:
     - uses: cachix/install-nix-action@v16
       with:
         nix_path: nixpkgs=channel:nixos-unstable
-    - run: nix-shell --run 'cabal update; make html SPHINXOPTS="-W"'
+    - run: nix-shell --run 'cabal update; make clean; make html SPHINXOPTS="-W"'
     - name: Deploy 🚀
       uses: JamesIves/github-pages-deploy-action@v4.2.2
       with: